Supplementary feeding restructures urban bird communities

Abstract

Food availability is a primary driver of avian population regulation. However, few studies have considered the effects of what is essentially a massive supplementary feeding experiment: the practice of wild bird feeding. Bird feeding has been posited as an important factor influencing the structure of bird communities, especially in urban areas, although experimental evidence to support this is almost entirely lacking. We carried out an 18-mo experimental feeding study at 23 residential properties to investigate the effects of bird feeding on local urban avian assemblages. Our feeding regime was based on predominant urban feeding practices in our region. We used monthly bird surveys to compare avian community composition, species richness, and the densities of local species at feeding and nonfeeding properties. Avian community structure diverged at feeding properties and five of the commonest garden bird species were affected by the experimental feeding regime. Introduced birds particularly benefitted, with dramatic increases observed in the abundances of house sparrow (Passer domesticus) and spotted dove (Streptopelia chinensis) in particular. We also found evidence of a negative effect on the abundance of a native insectivore, the grey warbler (Gerygone igata). Almost all of the observed changes did not persist once feeding had ceased. Our study directly demonstrates that the human pastime of bird feeding substantially contributes to the structure of avian community in urban areas, potentially altering the balance between native and introduced species.avian ecology | community composition | garden birds | human interactions | wildlife feeding

Garden Bird Feeding: Insights and Prospects from a North-South Comparison of This Global Urban Phenomenon

“…Galbraith et al (2015) found greater abundances of introduced house sparrows and spotted doves at feeders in Auckland and reduced abundances of native species such as gray gerygones. While feeders clearly attract greater numbers of the species using them, they may also reduce species richness in the avian community because of the predominance of introduced species.…”

“…Therefore, Australian feeder birds are far larger than those typically found at Northern Hemisphere feeders. In New Zealand, the situation is strongly influenced by the abundance of introduced species with the most common being house sparrows Passer domesticus (20-35 g), common blackbirds and common mynas Acridotheres tristis (82-140 g) with the only native species feeding on grain-based supplements being the silvereye Zosterops lateralis (9-17 g; Galbraith et al, 2015). In South Africa, while the diversity of birds visiting gardens is remarkably large-from diminutive waxbills (Estrildidae) to huge hornbills (Bucerotidae)-we could find no reliable data with which to compile a comparative list of the most common species observed at bird feeders.…”

“…Nonetheless, a growing number of important pioneering investigations are shedding light on the ecological influence of food supplements on the local community of birds. One recent study compared the changes in composition and abundance of the suburban bird community in Auckland, New Zealand over an 18-month period during which food was provided by householders, followed by its withdrawal (Galbraith et al, 2015). The results were dramatic for several of the species involved, with increased abundance of house sparrows and spotted doves Streptopelia chinensis-both introduced speciesduring the provisioning phase, while that of the native gray gerygone Gerygone igata was significantly lower.…”

“…Bird feeding is variously advocated as an essential conservation activity, a simple way for people to connect with nature in an urbanizing world, and a means for enhancing environmental awareness and psychological wellbeing (Schoech et al, 2008;Davies et al, 2012;Cox and Gaston, 2016). However, it has also been implicated in the spread of catastrophic avian diseases (e.g., Dhondt et al, 2007;Robinson et al, 2010), altering ecosystem structure (Galbraith et al, 2015), benefiting invasive species (Galbraith et al, 2015), changing predator-prey dynamics (Malpass et al, 2017), and even contributing to rapid evolutionary change (Bearhop et al, 2005). Furthermore, the possibility that birds may become dependent on anthropogenic food is a primary concern of both opponents to, and proponents of, bird feeding (e.g., Howard and Jones, 2004;Jones, 2011).…”

Food preferences by birds using bird-feeders in winter: a large-scale experiment

“…Generally, people support birds with food in winter not only for conservation purposes, but also for aesthetic reasons, and most providers of food would like to know what is the most preferred food (Lott 1988;Cox and Gaston 2015) to attract more birds (Cowie and Hinsley 1988;Galbraith et al 2014Galbraith et al , 2015Cox and Gaston 2015). Feeding birds is probably among the most popular animal-human interactions (Jones and Reynolds 2008), and producing and selling bird food is still an increasing market (Buczacki 2007;Jones and Reynolds 2008).…”